This invention relates to arrangements for retaining permanent magnets radially in position in permanent magnet rotors for electric machines operating at high speed.
Conventional arrangements for retaining magnets in position in rotors for electric machines include slot wedges which span the distance between adjacent pole pieces across the radially outer surface of the magnets. Such arrangements have limited centrifugal load carrying capability.
The Burson U.S. Pat. No. 4,179,634 discloses a magneto rotor having permanent magnets which are retained in a cavity formed in the rotor by pole pieces disposed on opposite sides of the magnet and retained by retaining pins received in axially extending slots in the pole pieces.
The Patent to Morill U.S. Pat. No. 2,516,901 discloses a permanent magnet rotor having a hub to which permanent magnets are affixed by screws engaging shoulders on the magnets. In addition, rings may be cast around the shoulders of the magnets and the screws to assist in retaining the magnets on the hub.
In the magneto shown in the Iwata et al. U.S. Pat. No. 5,811,908, U-shaped permanent magnet retention channels made of magnetic material have projections at the outer ends of the walls which are received in corresponding grooves in adjacent pole pieces.
According to the Tomite et al. U.S. Pat. No. 4,745,319, permanent magnets are secured to the inner surface of a surrounding yoke by attaching one surface of a U-shaped elastic retainer member to the inner surface of the yoke and attaching the ends of the U-shaped retainer to edges of adjacent magnets which are to be retained in the yoke.
Accordingly, it is an object of the present invention to provide a retaining arrangement for permanent magnets in a rotor for an electric machine which overcomes disadvantages of the prior art.
Another object of the invention is to provide a retaining arrangement for permanent magnets by which they are secured effectively in the radial direction during high speed operation of a rotor.
These and other objects of the invention are attained by providing a retaining arrangement in which permanent magnets are retained in a permanent magnet rotor by U-shaped retainers supported from a rotor rim, the retainers being made of nonmagnetic material and having a smooth channel to receive magnets and provide radial support. In one embodiment the U-shaped retainers have laterally outer surfaces which converge inwardly in the radially outward direction and the adjacent opposed pole pieces, which are affixed to the rotor rim, have corresponding lateral surfaces which converge inwardly in the radially outward direction. In another embodiment, the U-shaped retainer is connected to the rotor rim by fasteners such as screws.